JP2006031832A - Focus control method for optical disk recording/ reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus control method for an optical disk recording/reproducing device using a multilayer disk. <P>SOLUTION: In the optical disk recording/reproducing device using an optical disk equipped with at least first and second recording layers, the thickness of a spacer part between the first and second recording layers disposed in an optical disk 1 is measured, a defocusing amount with respect to the second recording layer is set on the basis of the measured spacer thickness, and a focus servo operation is carried out to focus a laser beam emitted from an optical pickup 2 on the second recording layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides a focus of an optical disc recording / reproducing apparatus that performs a read operation of a signal recorded on an optical disc with a laser beam irradiated from a laser diode incorporated in an optical pickup or a recording operation of a data signal onto the optical disc. It relates to a control method.

  2. Description of the Related Art Optical disc recording / reproducing apparatuses that perform a read operation of a signal recorded on an optical disc by a laser beam emitted from a laser diode and a recording operation of a signal on the optical disc are widely used. As an optical disk recording / reproducing apparatus, an apparatus using an optical disk called CD and an apparatus using an optical disk called DVD are generally used.

  Since there is a high demand for recording many signals on an optical disc, a transition from CD to DVD has been carried out. In this DVD disc, not only one recording layer but also two recording layers are provided. An optical disc called a two-layer disc has been developed.

In such an optical disk recording / reproducing apparatus using a two-layer disk, a technique for focusing each signal layer with a laser beam irradiated from an optical pickup has been developed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 10-188457

  In the technique described in Patent Document 1, the focus control operation for focusing the laser light emitted from the optical pickup on the two signal layers is accurate in the arrangement of the recording layer of the optical disk, that is, the physical property of the optical disk. This is done on the assumption that the characteristics are in accordance with the standard.

  However, a DVD-type optical disc is produced by bonding two discs having a predetermined thickness (0.6 mm). As a result, the thickness of the cover layer provided between the surface of the optical disc and the first recording layer can be made substantially constant, but the spacer portion that is the bonding portion of the two discs, that is, the first recording layer. The thickness of the spacer portion provided between the recording layer and the second recording layer is not constant and differs from disk to disk. As a result, there is a problem that an accurate focus servo operation cannot be performed with the defocus amounts set for the first recording layer and the second recording layer.

  The present invention intends to provide a focus control method capable of solving such a problem.

  The present invention measures the thickness of a spacer portion between a first recording layer and a second recording layer, sets a defocus amount for the second recording layer based on the measured spacer thickness, and an optical pickup. Is configured to perform a focus servo operation for focusing the laser light emitted from the second recording layer on the second recording layer.

The present invention also provides a memory circuit in which a defocus amount set corresponding to the spacer thickness is stored, and reads the defocus amount corresponding to the measured spacer thickness from the memory circuit. Configured to set.

  The present invention measures the interval of pulse signals obtained by binarizing the focus error signal generated from the photodetector with a predetermined threshold by moving the objective lens in the direction perpendicular to the surface of the optical disc. Thus, the spacer thickness is measured.

  In addition, the present invention provides a counter circuit that starts the count operation of the clock signal when the first pulse signal is obtained, and sets the spacer thickness based on the number of clock signals counted until the next pulse signal is obtained. It is configured to measure.

  Furthermore, the present invention is configured to generate a focus error signal for measuring the spacer thickness by moving the objective lens in the surface direction of the optical disk from a position away from the optical disk.

  The present invention also provides a maximum separation position restricting member that restricts the position at which the objective lens is separated from the optical disc surface, and moves the objective lens in the surface direction of the optical disc from the maximum separation position regulated by the maximum separation position restricting member. It is configured to let you.

  In the present invention, a maximum separation position regulating member that regulates the position where the objective lens is separated from the optical disk surface is provided, and the objective lens is moved in the surface direction of the optical disk from the maximum separation position regulated by the maximum separation position regulating member. A counter circuit that starts the counting operation of the clock signal when the movement of the objective lens is started from the maximum separation position, and the number of clock signals counted until the first pulse signal is obtained and the next pulse signal are The spacer thickness is measured based on the difference in the number of clock signals counted until it is obtained.

  Further, the present invention is configured to generate a focus error signal for measuring the spacer thickness by moving the objective lens from a position close to the optical disk in a direction away from the optical disk surface.

  Furthermore, the present invention provides a closest approach position restricting member for restricting a position where the objective lens approaches the optical disk surface, and the objective lens is moved away from the optical disk surface from the closest position restricted by the closest approach position restricting member. Is configured to move.

  In the present invention, a closest approach position restricting member for restricting a position where the objective lens approaches the optical disk surface is provided, and the objective lens is moved away from the optical disk surface from the closest approach position restricted by the closest approach position restricting member. The counter circuit that starts counting the clock signal when the objective lens starts moving from the closest position is provided, and the number of clock signals counted until the first pulse signal is obtained and the next pulse The spacer thickness is measured based on the difference in the number of clock signals counted until a signal is obtained.

  The present invention measures the thickness of a spacer portion between a first recording layer and a second recording layer, sets a defocus amount for the second recording layer based on the measured spacer thickness, and an optical pickup. Since the focus servo operation for focusing the laser beam emitted from the second recording layer on the second recording layer is performed, an accurate focus control operation can be performed.

  Further, the present invention measures the interval of pulse signals obtained by binarizing the focus error signal generated from the photodetector with a predetermined threshold by moving the objective lens in the direction perpendicular to the surface of the optical disc. Therefore, the thickness of the spacer portion can be easily measured.

  In the present invention, the defocus amount for performing the focus servo operation is set by measuring the thickness of the spacer portion between the first recording layer and the second recording layer.

  FIG. 1 is a block circuit diagram showing an embodiment of an optical disc recording / reproducing apparatus according to the present invention, FIG. 2 is an explanatory diagram showing the relationship between the optical disc according to the present invention and laser light, and FIG. 3 explains the operation of the present invention. FIG. 4 is a signal waveform diagram for explaining the operation of the present invention.

  In FIG. 1, reference numeral 1 denotes an optical disk that is rotationally driven by a spindle motor (not shown). For example, the optical disk 1 is configured to be rotationally controlled so as to have a constant linear velocity, and as shown in FIG. A layer L1 and a second recording layer L2 are provided. Reference numeral 2 denotes an optical pickup in which a laser diode (not shown) for irradiating a laser beam is incorporated. From the objective lens 3 and the optical disc 1 for focusing the laser beam emitted from the laser diode on the recording layer of the optical disc 1. The reflected laser beam is received and converted into an electrical signal, and the photodetector 4 composed of a quadrant sensor or the like, the tracking coil 5 for displacing the objective lens 3 in the radial direction of the optical disc 1, and the objective lens 3 for the optical disc 1 A focusing coil 6 that is displaced in the direction perpendicular to the signal plane is incorporated.

  Reference numeral 7 denotes a maximum separation position regulating member that comes into contact with a lens holder (not shown) that supports the objective lens 3 when the objective lens 3 is farthest from the surface of the optical disk 1 by the drive signal supply operation to the focusing coil 6. The objective lens 3 is provided so as to regulate the maximum separation position from the optical disc 1. Reference numeral 8 denotes a closest approach position regulating member that comes into contact with a lens holder that supports the objective lens 3 when the objective lens 3 comes closest to the surface of the optical disc 1 by supplying a driving signal to the focusing coil 6. It is provided so as to regulate the closest position to the optical disc 1.

  Reference numeral 9 denotes an optical output signal processing circuit to which an electric signal obtained from the photodetector 4 is input as an optical signal, which indicates a tracking error signal indicating a shift of the laser light with respect to the signal track and a focus shift of the laser light with respect to the recording layer. A reproduction signal which is a read signal of a focus error signal and a signal recorded on the optical disc 1 is generated. Since various signal generation operations by the optical output signal processing circuit 9 are performed by known circuits, description thereof is omitted.

  Reference numeral 10 denotes a tracking servo circuit to which a tracking error signal generated and output by the optical output signal processing circuit 9 is input, and supplies a tracking coil drive signal based on the input tracking error signal to the tracking coil 5. Is configured to perform a tracking control operation. Reference numeral 11 denotes a focus servo circuit to which a focus error signal generated and output by the optical output signal processing circuit 9 is input, and supplies a focus coil drive signal based on the input focus error signal to the focusing coil 6. Is configured to perform a focus control operation.

Reference numeral 12 denotes a digital signal processing circuit which receives a reproduction signal binarized by a binarization circuit provided in the optical output signal processing circuit 9 and performs digital signal processing, and demodulates various signals. It is configured as follows. Reference numeral 13 denotes a control circuit for controlling each operation of the optical disk recording / reproducing apparatus. By using the synchronization signal generated by the digital signal processing circuit 12, the rotation control operation of the optical disk 1 by the spindle motor and the processing of the reproduction signal and the recording signal are performed. It is configured to control operation and signal transmission / reception operation with a host device such as an external personal computer. Such a control circuit 13 is configured by a microcomputer and is configured to perform various control operations based on program software stored in a ROM or the like provided therein.

  Reference numeral 14 denotes a comparator circuit to which the focus error signal output from the optical output signal processing circuit 9 is input. A signal of H (high) level is output to the control circuit 13 during the period when the level of the focus error signal exceeds the threshold value VR. It is comprised so that it may output. FIG. 3A shows the relationship between the focus error signal obtained when the objective lens 3 is approached from a position away from the recording layer provided on the optical disc 1 and the threshold value VR. The signal will change to an S shape as is well known. Such S-shaped changes will appear as two S-shaped changes when the optical disk 1 has two layers. FIG. 3B shows a pulse signal output from the comparator circuit 14, and an H level signal is output for a period exceeding the threshold value VR.

  Reference numeral 15 denotes a counter circuit whose operation is controlled by the control circuit 13. When a pulse signal is output from the comparator circuit 14, the counter circuit starts a count operation and when the next pulse signal is output, the first pulse signal and the next pulse signal are output. It is comprised so that the space | interval between other pulse signals may be measured. In such a measurement operation, for example, a clock signal generation circuit that generates a clock signal of a predetermined frequency is provided, and the interval can be measured by the number of clock signals counted between the pulse signals.

  Reference numeral 16 denotes a spacer thickness measuring circuit for obtaining the thickness of the spacer portion S provided between the first recording layer L1 and the second recording layer L2 based on the number of clock signals counted by the counter circuit 15. Yes, since it can be obtained from the relationship between the number of clock signals set in advance and the thickness, data based on the obtained thickness is output to the control circuit 13.

  A memory circuit 17 is controlled by the control circuit 13 and stores data indicating the defocus amount with respect to the thickness of the spacer portion S as table data. Here, the focus control operation of the laser beam irradiated from the optical pickup 2 to the optical disc 1 will be described. When the focus coil drive signal is supplied from the focus servo circuit 11 to the focusing coil 6 and the objective lens 3 is displaced in the direction perpendicular to the surface of the optical disc 2, the optical output signal processing circuit 9 as shown in FIG. An S-shaped focus error signal is generated and output. This is the point at which the zero-cross point F of the S-shaped focus error signal is determined to be in focus from the laser light irradiation spot irradiated on the photodetector 4, but is optimal for the recording layer of the optical disc 2. It cannot be determined that it is the focal point.

  That is, the positional relationship between the optical disk 1 and the optical pickup 2 placed on a turntable (not shown), the error in the mounting position of each optical component and the photodetector 4 in the optical pickup 2, etc. This is because the zero-cross point F of the S-shaped focus error signal does not become the optimum focal point for the recording layer of the optical disc 2. In order to improve such a point, a setting operation for shifting the in-focus point for performing the focus servo operation by the focus servo circuit 11 to the best point, that is, a defocus amount setting operation is performed. Such a defocus amount setting operation is performed by a control operation for the focus servo circuit 11 by the control circuit 13.

  2A shows a state in which a focus control operation is performed on the first recording layer L1, and the laser light focused by the objective lens 3 is focused on the first recording layer L1 through the cover layer C. FIG. It will be. FIG. 2B shows a state in which a focus control operation is performed on the second recording layer L2, and the laser light focused by the objective lens 3 passes through the cover layer C, the first recording layer L1, and the spacer portion S. The focus is on the second recording layer L2.

  In such a configuration, the defocus amount setting operation for the first recording layer L1 is performed by using the test disc when the optical disc recording / reproducing apparatus is manufactured, because the thickness of the cover layer C is a substantially prescribed thickness. . Such an operation of setting the defocus amount can be detected and set by adjusting the level of the drive signal supplied to the focusing coil 6 so that the level of the reproduction signal obtained from the photodetector 4 is maximized. I can do it. In addition, detection and setting can be performed by adjusting the level of the drive signal supplied to the focusing coil 6 so that the jitter value included in the signal reproduced from the optical disk is minimized.

  Further, in the case where the focus characteristic for the recording operation is emphasized in addition to the setting of the defocus amount by the above-described method, the β value obtained from the RF signal obtained by recording the test signal on the recording layer and reproducing the recorded signal The optimum defocus amount can be set by setting so that the value of becomes the highest. This β value is calculated as β = (A1 + A2) / (A1−A2) where A1 is the positive peak level of the RF signal and A2 is the negative peak level.

  The defocus amount setting operation for the second recording layer L2 is set similarly to the first recording layer L1, but the thickness of the spacer portion S between the first recording layer L1 and the second recording layer L2 is set. The operation of detecting the relationship between the value and the defocus amount and storing the data indicating the correction amount for the thickness in the memory circuit 17 is performed when the optical disc recording / reproducing apparatus is manufactured.

  Although the defocus amount setting operation is performed as described above, the operation for measuring the thickness of the spacer portion S will be described next. A focus drive signal is supplied from the focus servo circuit 11 to the focusing coil 6, and the drive signal is supplied to the optical disk 1 after a signal for temporarily moving the objective lens 3 in a direction away from the surface of the optical disk 1. It is performed so as to move toward the surface.

  When such an operation is performed, the objective lens 3 is moved in a direction approaching from a position away from the surface of the optical disc 1 in a state where the laser light generated from the laser diode is irradiated. When such an operation is performed, the focus error signal shown in FIG. 3A is output from the light output signal processing circuit 9 every time the focal point of the laser light passes through the first recording layer L1 and the second recording layer L2. At the same time, the pulse signal shown in FIG. 3B is output from the comparator circuit 14.

  FIG. 4 shows the relationship of pulse signals output from the comparator circuit 14 when the objective lens 3 is displaced from a position separated from the optical disk 1 to a position approached in order to measure the thickness of the spacer portion S. Yes, the pulse signal P1 corresponds to the first recording layer L1, and the pulse signal P2 corresponds to the second recording layer L2.

  When the pulse signal P1 is output from the comparator circuit 14, the control circuit 13 performs a control operation on the counter circuit 15. As a result, the counter circuit 15 counts the number of clock signals output from the clock signal generation circuit. Start. When such a counting operation is performed, when the next pulse signal P2 is output from the comparator circuit 14, the control operation for the counter circuit 15 by the control circuit 13 is performed. Such a control operation stops the counting operation of the clock signal by the counter circuit 15 and sets the number of clock signals counted until the pulse signal P2 is output after the pulse signal P1 is output from the comparator circuit 14 as a spacer. Output to the thickness measurement circuit 16.

The number of clock signals counted by the above-described operation is the number of clocks obtained in the period indicated by T in FIG. 4, and the number is proportional to the thickness of the spacer portion S. Therefore, by setting the thickness of the spacer portion S in advance corresponding to the number of clocks, the thickness of the spacer portion S can be recognized as data. When data indicating the thickness of the spacer portion S is output from the spacer thickness measuring circuit 16 to the control circuit 13, the defocus amount stored in the memory circuit 17 is read corresponding to the data, and the defocus amount is read. A setting operation for the focus servo circuit 11 is performed to perform a focus servo operation based on the focus amount.

  As a result of performing the defocus amount setting operation for the focus servo circuit 11, the focus control operation for the second recording layer L2 can be performed accurately. As a result, the reproduction operation of the signal recorded on the second recording layer L2 and the recording operation of the signal on the second recording layer L2 can be performed in an optimum state.

  The above-described thickness measurement operation of the spacer portion S is performed by displacing the objective lens 3 in a direction in which the objective lens 3 is approached from a position separated from the surface of the optical disc 1. It is also possible to measure by displacing in a direction away from the position approaching. In this case, after the pulse signal P2 corresponding to the second recording layer L2 is first output from the comparator circuit 14, the pulse signal P1 corresponding to the first recording layer L1 is output.

  Further, in order to measure the thickness of the spacer portion S, when the objective lens 3 is displaced in the direction of approaching from the position separated from the surface of the optical disc 1, the lens holder contacts the maximum separation position restricting member 7 with the lens holder. By displacing to the contact position, it is possible to define the displacement start position of the objective lens 3 for starting measurement. On the other hand, when the objective lens 3 is displaced in a direction away from the position where the objective lens 3 approaches the surface of the optical disc 1 in order to measure the thickness of the spacer portion S, the objective holder 3 is moved to the closest position restricting member 8 by the lens holder. If the position of the objective lens 3 is displaced to a position where it is in contact with the objective lens 3, it is possible to define the displacement start position of the objective lens 3 for measuring the spacer thickness.

  As described above, the measurement operation between the pulse signal P1 and the pulse signal P2 performed for measuring the thickness of the spacer portion S by the counter circuit 15 is performed. Next, a different measurement method will be described.

  As described above, when the objective lens 3 is moved in the surface direction of the optical disc 1 from the position regulated by the maximum separation position regulating member 7 in order to measure the thickness of the spacer portion S, the comparator is similar to the above-described operation. A pulse signal P1 and a pulse signal P2 are output from the circuit 14.

  When the objective lens 3 starts moving from the maximum separation position, the counter circuit 15 starts counting the clock signal, and the number of clock signals counted until the pulse signal P1 is output and the pulse signal P2. The operation of counting the number of clock signals that are counted until the signal is output is performed.

  When such a clock signal counting operation is performed, the number of clocks C1 and the position of the second recording layer L2 counted during the period T1 until the objective lens 3 moves from the maximum separation position to the position of the first recording layer L1. The number of clocks C2 counted in the period T2 until the movement can be measured. Therefore, the number of clocks counted in the period T between the first pulse signal P1 and the second pulse signal P2 from C2-C1 can be obtained.

The number of clocks obtained in this way is proportional to the thickness of the spacer portion S. Therefore, by setting the thickness of the spacer portion S in advance corresponding to the number of clocks, the thickness of the spacer portion S can be recognized as data. When data indicating the thickness of the spacer portion S is output from the spacer thickness measurement circuit 16 to the control circuit 13,
A defocus amount stored in the memory circuit 17 can be read corresponding to the data, and a setting operation for the focus servo circuit 11 can be performed to perform a focus servo operation based on the defocus amount.

  As described above, the thickness of the spacer portion S can be measured by moving the objective lens 3 from the position regulated by the maximum separation position regulating member 7 in the surface direction of the optical disc 1. The thickness of the spacer portion S can be measured by moving in a direction away from the surface of the optical disc 1 from the position restricted by the closest approach position regulating member 8.

  In this embodiment, the optical disk having two recording layers has been described. However, the present invention can be applied to an optical disk recording / reproducing apparatus using an optical disk having three or more recording layers.

1 is a block circuit diagram showing an embodiment of an optical disc recording / reproducing apparatus according to the present invention. It is explanatory drawing which shows the relationship between the optical disk which concerns on this invention, and a laser beam. It is a signal waveform diagram for demonstrating operation | movement of this invention. It is a signal waveform diagram for demonstrating operation | movement of this invention.

Explanation of symbols

1 Optical disc
2 Optical pickup
3 Objective lens
4 photodetectors
6 Focusing coil
7 Maximum separation position restricting member
8 Closest position restriction member
9 Optical output signal processing circuit 11 Focus servo circuit 13 Control circuit 14 Comparator circuit 15 Counter circuit 16 Spacer thickness measurement circuit 17 Memory circuit

Claims (10)

A focus control method for an optical disc recording / reproducing apparatus configured to use an optical disc having at least a first and a second recording layer and perform a signal recording / reproducing operation by a laser beam irradiated from the first recording layer side. Measure the thickness of the spacer portion between the first recording layer and the second recording layer, set the defocus amount for the second recording layer based on the measured spacer thickness, and irradiate from the optical pickup A focus control method for an optical disc recording / reproducing apparatus, characterized in that a focus servo operation for focusing a laser beam on the second recording layer is performed. A memory circuit that stores the defocus amount set according to the spacer thickness is provided, and the defocus amount is set by reading the defocus amount corresponding to the measured spacer thickness from the memory circuit. The focus control method according to claim 1. The spacer thickness is measured by measuring the interval of pulse signals obtained by binarizing the focus error signal generated from the photodetector with a predetermined threshold by moving the objective lens in the direction perpendicular to the surface of the optical disk. The focus control method according to claim 1, wherein the focus control method is performed. A counter circuit that starts counting the clock signal when the first pulse signal is obtained is provided, and the spacer thickness is measured based on the number of clock signals counted until the next pulse signal is obtained. The focus control method according to claim 3. 4. The focus control method according to claim 3, wherein the focus error signal is generated by moving the objective lens in a surface direction of the optical disc from a position away from the optical disc. A maximum separation position restricting member that restricts the position at which the objective lens is separated from the optical disk surface is provided, and the objective lens is moved in the surface direction of the optical disk from the maximum separation position regulated by the maximum separation position restriction member. The focus control method according to claim 5, wherein: A maximum separation position restricting member for restricting the position where the objective lens is separated from the optical disk surface is provided, and the objective lens is moved in the surface direction of the optical disk from the maximum separation position regulated by the maximum separation position restricting member. A counter circuit is provided to start the clock signal counting operation when the objective lens starts moving, and the number of clock signals counted until the first pulse signal is obtained and counted until the next pulse signal is obtained. 4. The focus control method according to claim 3, wherein the spacer thickness is measured based on a difference in the number of clock signals. 4. The focus control method according to claim 3, wherein the focus error signal is generated by moving the objective lens in a direction away from the optical disk surface from a position close to the optical disk. A closest approach position restricting member that restricts the position where the objective lens approaches the optical disk surface is provided, and the objective lens is moved in a direction away from the optical disk surface from the closest approach position restricted by the closest approach position restricting member. The focus control method according to claim 8. A closest approach position restricting member that restricts the position at which the objective lens approaches the optical disk surface is provided, and the objective lens is moved away from the optical disk surface from the closest approach position controlled by the closest approach position restricting member. A counter circuit is provided to start the clock signal counting operation when the objective lens starts moving from the position. The number of clock signals counted until the first pulse signal is obtained and the next pulse signal are obtained. 4. The focus control method according to claim 3, wherein the spacer thickness is measured based on a difference in the number of counted clock signals.

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